Figure 7. Effect of lignin dosage on the oxidation reaction.
Reaction condition: 10 g (12 mL) microemulsion (WW:WO :WP = 15.7 :9.2 :75.1,wt. %), 0.1 mmol CuSO4, 25.0 mmol
L-1 H2SO4, 1 MPa
O2, 433 K, 4 h.
The effect of initial lignin dosage on its own oxidation in the
microemulsion reactor (point c in Figure 3) was studied to investigate
the capacity of this novel reactor under the optimized reaction
conditions. It is clearly seen in Figure 7, that the
total mass of phenolic monomers
grows linearly with the increasing mass of lignin. When the lignin
dosage changes from 0.1 to 0.5 g, the total mass of phenolic monomers
grows from 12.7 to 57.7 mg, while the loss of total yield of phenolic
monomers is no more than 10% (127.1 to 115.1 mg g-1).
This demonstrates that this SFME reactor is efficient with a remarkable
capacity up to 40.8 g
L-1 at 0.5 g lignin dosage, even by the comparison to
the outstanding works about the oxidation of lignin in ionic liquid or
aqueous system (12.5 and 10 g L-1respectively).9, 46 Moreover, by consideration of
lignin solubility in this system (79.1 g L-1), the
capacity of the microemulsion reactor can be much higher for lignin
oxidation, since the maximum concentration (40.8 g
L-1) is just near to half of its solubility in this
study.